1. Field of the Invention
The present invention relates to an imaging-device driving unit which drives an imaging device according to the emission pattern of illumination light.
2. Description of the Related Art
An electronic endoscope having an imaging device at a head end of an insertion tube is known. By transmitting illumination light emitted by the light source to the head end of an insertion tube through an optical fiber, a subject in a dark area such as one inside the body, or an internal mechanism, can be photographed and/or filmed.
An image with a special visible effect can be displayed by using a special illumination method on a subject. For example, in a known technique, a subject is illuminated by pulses of light generated by pulse emission. By filming the vocal cords illuminated by pulses of light at a frequency adjusted to be nearly the same as the vibration of the vocal cords, an image of the quickly vibrating vocal cords, can be generated such that they appear to vibrate slowly.
If a user desires to observe a rapidly moving subject, then the user will usually select pulsed light. Accordingly, it is preferable for all the pixels to receive light simultaneously in order to capture an optical image of the subject using pulsed light illumination. On the other hand, if a user desires to observe a still or slowly moving subject, the user will select continuous light. Accordingly, when using continuous light illumination, it is preferable to generate an image signal in which noise in the captured image is reduced.
In order to film a subject with global exposure and also reduce noise, prior electronic endoscope has typically employed CCD imaging devices. However, some problems include high manufacturing cost of the CCD imaging device, high voltage requirement to drive the CCD imaging device, and requirement of many signal lines in a CCD imaging device.
To solve such problems, Japanese Unexamined Patent Publication No. 2002-58642 proposes that a CMOS imaging device with its lower power consumption and manufacturing cost than a CCD imaging device, be used in an electronic endoscope. However, there is the problem of a higher signal-to-noise ratio in the image signal generated by a CMOS imaging device when global exposure is used. Accordingly, when a CMOS imaging device is used to generate an image signal with global exposure, noise in a displayed image becomes conspicuous when a subject is illuminated by continuous light as compared to pulsed light.